ω phase acts as a switch between dislocation channeling and joint twinning- and transformation-induced plasticity in a metastable β titanium alloy

By M. Lai, T. Li, Dierk Raabe. Acta Materialia, 2018

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Abstract We have investigated the twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) as well as the influence of ω phase on these two phenomena in a metastable β-type Ti–25Nb–0.7Ta–2Zr (at.%) alloy. We set off with two starting states: one is ω-free and the other one contains a high number density (3.20 ± 0.78 × 1024 m−3) of nanometer-sized (∼1.23 nm) ω particles. Deformation experiments demonstrate that the plastic deformation of the ω-free alloy is mediated by stress-induced β → α" martensitic transformation, {332} twinning and dislocation slip, where the former two induce joint TRIP and TWIP effects and the latter one carries the majority of the plastic strain. In the ω-enriched alloy, the ω particles fully suppress the TWIP and TRIP effects and promote localization of dislocation plasticity into specific ω-devoid channels. Atom probe tomography analysis reveals that the elemental partitioning between β and ω results in only subtle enrichment of solutes in the β matrix, which cannot sufficiently stabilize the matrix to prevent martensitic transformation and twinning. A new mechanism based on the shear modulus difference between β and ω is proposed to explain the suppression of TRIP and TWIP effects by ω particles.

Subfields: Materials Chemistry, Mechanical Engineering, Mechanics of Materials

View Paper: https://www.semanticscholar.org/paper/407b4e65f7fb67f774904a152d376d963bf3a949